An exhaust system usually comprises an exhaust line carrying exhaust gas away from the internal combustion engine and at least one exhaust gas treatment device such as a catalyst, a particulate filter and a muffler as well as combinations thereof arranged in the exhaust line. In addition, an exhaust system may also have an injection device for injecting a liquid educt into the exhaust line, usually arranged upstream from an exhaust gas treatment device on the exhaust line. For example, a fuel may be injected into the exhaust line upstream from an oxidation catalyst to trigger an exothermic combustion reaction on the oxidation catalyst. For example, an oxidation catalyst arranged near the motor can be brought rapidly to its operating temperature in this way to thereby reduce pollution emissions in a cold start of the internal combustion engine. In addition, heat can thereby be introduced into the exhaust line, e.g., to heat a particulate filter arranged downstream from the oxidation catalyst to a regeneration temperature. Likewise, with such an injection device a reducing agent, e.g., ammonia can be sprayed into the exhaust stream to reduce nitrogen oxides entrained by the exhaust gas in an SCR catalyst arranged downstream. Instead of ammonia, urea and/or an aqueous urea solution may also be sprayed into the exhaust stream. A hydrolysis reaction creates ammonia and water from the urea-water solution. The ammonia thereby produced can be utilized again in an SCR catalyst to reduce the nitrogen oxides in the exhaust gas. Furthermore, with the help of the injection device, fuel or another suitable reducing agent may be sprayed into the exhaust stream upstream from an NOX storage catalyst to induce regeneration of the NOX storage catalyst.
To improve and/or allow the action of the educt that is sprayed into the exhaust line in liquid form, extensive evaporation is desirable, as is intense and thorough mixing with the exhaust gas to homogenize the exhaust gas-educt mixture. Accordingly the exhaust system can be equipped with a mixing and/or evaporation system arranged in the exhaust line downstream from the injection device and upstream from the respective exhaust gas treatment device.
The respective exhaust line in which the exhaust gas treatment device, the injection device and the mixing and/or evaporation device are installed is usually assembled from several components, e.g., multiple pipe bends, at least one exhaust manifold and several exhaust pipes which together form a section of the exhaust line that carries the exhaust gas. With an assembled design, such an exhaust pipe may protrude at an end section into another nearby pipe or into a housing of an exhaust gas treatment device.